The invention relates to metal articles with fine uniform structures and textures and methods of making such articles. In particular, metal articles of type described are especially useful as sputtering targets.
Sputtering targets of high purity metals and alloys are widely used in electronics and semiconductor industries for sputtering thin films. It is desirable to obtain large size targets.
In accordance with the invention there is provided a high purity tantalum article, such as a sputtering target having substantially uniform texture. In particular, the invention comprises a tantalum sputtering target of at least about 99.95% tantalum and a substantially uniform {100} crystallographic orientation.
A process to provide the tantalum sputtering target is disclosed in application Ser. No. 09/098,761 filed on even date herewith, the disclosure of said application is expressly incorporated herein by reference. The process comprises:
1) providing a metal billet;
2) heating the billet to a forging temperature below the recrystallization temperature of the metal;
3) applying a solid lubricant between the ends of the billet to be forged and press plates of a forging machine in which the billet is to be forged to reduce the friction during forging;
4) forging the billet to a desired billet thickness with about 70% to 95% reduction;
5) bringing the forged billet to about room temperature;
6) rolling the billet to plate with a reduction in thickness per rolling pass sufficient to provide near uniform strain distribution; and
7) recrystalization annealing the plate.
It is also advantageous to machine shallow pockets in both ends of the billet ends prior to applying the solid lubricant of sufficient thickness. Preferably, the billet is forged at a temperature below the minimum temperature of static recrystallization and then rolled and annealed at a time and temperature to provide the beginning stage of static recrystallization.
The rolling reduction per pass is desirably in accordance with a relationship of the minimum reduction per pass, the roll diameter and the desired billet thickness after forging. Generally, the reduction per pass during rolling is about 10% to 20% per pass.
Another embodiment the invention comprises a metal article, such as a sputtering target, having a near-to-minimum of statically crystallized grain size, and uniform texture.
The present process can be applied to different metals and alloys that display good ductility and workability at temperatures below corresponding temperatures of static recrystallization. Among metals with which the invention can be applied are Al, Ti, Ta, Cu, Nb, Ni, Mo, Au, Ag, Re, Pt and other metals, as well as their alloys. One embodiment of the method comprises the steps of processing an ingot to a semi-finished billet, including, for example, melting, ingot casting, homogenizing/solutionizing heat treatment, hot working to break down the cast structure, and billet preparation followed by billet shaping and thermomechanical treatment to fabricate a product, for example a sputtering target, and refine the metallurgical structure and produce a desired texture. By one embodiment of the process of the invention, cold/warm working and annealing are used to develop extremely fine, uniform structures and strong, uniform textures that result in improvement in performance of sputtering targets.